Well if you hold onto your DSi for a little while longer you can transfer over some of your favorite DSiWare games, then get rid of it. If you for some reason still want to hold onto your 3DS, then pull out a bunch of old games and sell them on Ebay or something.

I got a deal that looks like this. I'm getting a €60 discount if I turn in my DS Lite. My touchscreen got some scratches so I don't think I'll get that money for it when I sell it online. So I guess it kind of depends on in what condition it is?